1. Field of the Invention
The invention relates generally to charge air coolers and particularly to a charge air cooler for motor vehicles.
2. Description of the Related Art
A typical prior art air cooler is described in the Shell Lexikon Verbrennungsmotoren (Shell Dictionary of Internal Combustion Engines), supplement to ATZ (Automotive Engineering Journal) and MTZ (Engine Engineering Journal), series 33. It consists of a finned-tube block, which is connected to a charge air inlet chamber and to a charge air outlet chamber. In this arrangement, hot charge air can flow from an internal combustion engine of the motor vehicle through flat tubes of the finned-tube block. A large proportion of the heat is transferred to the ambient air via fins arranged between the flat tubes and subjected to the action of ambient air. Within the flat tubes, there is an internal fin member which possesses rows of webs and web crosspieces. The rows are curved in the manner of webbed fins and offset relative to one another by predetermined distances. This ensures mixing of the charge air within the flat tubes.
A disadvantage of such a charge air cooler is that, within a particular row between two webs, a hot core flow remains behind in the region of the core of the flow, from which virtually no heat transfer to the internal fin member takes place. This occurs even though the charge air undergoes good heat transfer to the internal fin member in the boundary layer region. Overall, then, the actual heat transfer performance is less than the theoretically possible heat transfer performance.
Another related reference is DE 196 54 367 A1 and its corresponding publication U.S. Pat. No. 6,070,616, which discloses a method for attaching vortex generators in the form of winglets to a thin metal sheet. The vortex generators are shaped from the thin metal sheet by massive forming.
An object of the invention is to improve a charge air cooler of the type discussed above, in such a way that the heat exchange is improved over the entire flow profile and the hot core flow is passed to the internal fin member.
According to the first embodiment of the invention, at least one web and/or one web crosspiece of the internal fin member introduced into the flat tubes possesses at least one vortex generator. As a result, improved mixing of the hot core flow with the boundary layer flow is achieved. This is accomplished by a transverse flow in which the heat of the core flow is no longer guided by the internal fin member and the boundary layer flow guided in isolation by the wall of the flat tube. That is, the boundary layer flow is deliberately broken up and mixed. In addition to the simple breaking-up of the boundary layer flow, lengthwise vortexes are formed by the vortex generators, especially by the winglets. This causes the mixing action to extend far into the core flow. This enables the heat of all the charge air to be removed more efficiently to the ambient air.
In an another embodiment of the invention, the vortex generators are designed in the form of winglets, as a ramp or in the form of a tab. In these arrangements, the longitudinal axis of the winglets extends obliquely relative to the main flow direction of the charge air, in particular at an angle of approximately 15xc2x0 to 45xc2x0. As a result of such an arrangement of the winglets and the adjustment of the angle of the oblique position, control can be selectively exerted on the shape of the lengthwise vortex and hence, on the mixing of the flow.
In a further embodiment of the invention, consecutive webs in the main flow direction of the charge air have oppositely oriented winglets. As a result, after a lengthwise vortex with a particular direction of rotation is generated by a first winglet, a lengthwise vortex in the opposite direction is generated at the next winglet.
This further increases the efficiency of mixing.
In another embodiment of the invention, the winglets are arranged in pairs and extend in opposite directions obliquely to the main flow direction of the charge air, extending away from one another in the main flow direction of the charge air. The winglets are produced by shaping the webs and/or web crosspieces.
In a further embodiment of the invention, every second web of a row has a winglet oriented in the same direction. This is particularly beneficial in regards to manufacturing. It allows one row at a time to be demolded in parallel and hence, guarantees the simplest and most cost-effective design possible for the internal fin members.
In another embodiment of the invention, the vortex generator is designed in the form of a ramp inclined obliquely relative to the main flow direction of the charge air. In particular, the incline is at an angle of approximately 20xc2x0 to 30xc2x0. The air flow is deflected upward and downward by the ramp. In addition, a vortex flow with a significant transverse component is generated. This transverse component prevents the formation of a continuous core flow.
In a further embodiment of the invention, ramps ascending in the main flow direction of the charge air are followed by ramps descending in the main flow direction of the charge air. As a result, the air flow, as it passes through the fin member, is alternately deflected upward with one component and downward with the next component. This results in further turbulence and reduction of a continuous core flow.
Examples of embodiments of the invention are shown in the drawings and are described in detail below.